This invention relates to a sliding door such as a single sliding door or a double sliding door, and more particularly to a sliding door for air-tightly selectively closing an entrance of a large-sized freezer, a large-sized refrigerator, a freezing storehouse, a refrigerating storehouse, a clean room or the like which is mainly used for business purpose.
The inventor proposed a sliding door of such a type as disclosed in Japanese Patent Application Laid-Open Publication No. 52072/1993. The sliding door proposed is generally constructed in such a manner as shown in FIGS. 7 and 8.
More particularly, the sliding door proposed includes a door body 101 and bracket assemblies A'. The bracket assemblies A' each including a first bracket a1' which is formed at a lower portion thereof with a first groove and has a rolling wheel 110 rotatably supported in the first groove and a second bracket a2' which is arranged at a predetermined inclination angle and provided at an upper end thereof with an elastic suspension 111. The elastic suspension 111 is arranged in a manner to be slanted at the same angle as the second bracket a2' and includes an extensible rod 111a. The first and second brackets a1' and a2' are connected to each other through the extensible rod 111a of the elastic suspension 111.
In each of the bracket assemblies A', the second bracket a2' is mounted at a lower portion thereof on an upper portion of the door body 101. The sliding door also includes a rail 112 including an upper rail surface 112a and a lower rail surface 112b and horizontally rigidly arranged on a wall of an object such as a refrigerator or the like to be operated by the sliding door (hereinafter also merely referred to as "object") above an entrance 104 of the object. The lower rail surface 112b of the rail 112 is formed so as to be slanted at the same angle as the inclination angle of the second bracket a2. The rolling wheel 110 is carried on the upper rail surface 112a of the rail 112, so that the door body 101 may be suspended by upward elastic force of the elastic suspension 111 while being kept raised from a floor 3 on which the object is installed. The sliding door proposed further includes a third bracket b which is fixed at a lower portion thereof on an upper end of the door body 101 and on which a driving wheel 113 is rotatably supported while being slanted at the same angle as the inclination angle of the bracket a2'. The driving wheel 113 is pressedly abutted against the lower rail surface 112b of the rail 112 by upward elastic force of the elastic suspension 111. Such abutment of the driving wheel 113 against the lower rail surface 112b permits a degree of raising of a bottom packing of the door body 101 from the floor 103 to be controlled by the elastic suspension 111. The degree of raising of the bottom packing 107 is set to be smaller than a downward slanting section 114.
Also, in the proposed sliding door, the lower rail surface 112b of the rail 112 is formed on a portion thereof opposite to the driving wheel 113 of the door body 101 when the door body 101 is moved to an entrance closed position at which the door body 101 closes the entrance 104 of the object with a tapered section 109 on which the driving wheel 113 strikes to extend the extensible rod ilia against upward elastic force of the elastic suspension 111, resulting in the door body 101 being forcibly moved in an obliquely inward and downward direction.
The proposed sliding door constructed as described above actually exhibits significant advantages as compared with a conventional sliding door. More specifically, the conventional sliding door is large-sized and constructed into a heat insulating structure, resulting in being substantially increased in thickness and weight. Also, the conventional sliding door is required to airtightly close the object. For this purpose, a packing arranged around a door body of the door is elastically closely contacted with a wall the object around an entrance of the object and a floor thereof when the object is closed by the door. Unfortunately, this requires highly increased force at both initiation of a door opening operation and termination of a door closing operation. The above-described sliding door proposed by the inventor substantially eliminates such disadvantages encountered with the conventional one.
Nevertheless, the proposed sliding door has a disadvantage of still requiring force of a relatively large level due to frictional resistance between the packing of the door body and an outer wall surface of the object at the time of initiation of a door opening operation and termination of a door closing operation. This results in arrangement of a motor of a relatively increased capacity to be often required. Thus, it would be highly desirable to develop a sliding door which is capable of facilitating the opening and closing operation by hand or by means of a down-sized motor of a reduced capacity.